The Tokyo District Court on Wednesday sentenced a woman to 11 years in prison for throwing her 5-year-old son to his death from their 13th-floor apartment in Tokyo in 2014.

In handing down the ruling on 35-year-old Ai Kato, presiding Judge Hiroaki Saito said, “It is absolutely unthinkable that the boy could have unlocked and opened the window and fallen out by himself,” rejecting the defendant’s claim that his death was an “accident.”

Kato initially admitted to the murder charge during investigations but later denied the allegation. Saito said Kato’s “confession during investigations was detailed and credible.”

According to the ruling, Kato pushed her son Koki Takahashi, who was asleep, out of their apartment window around 11 p.m. on Dec. 29, 2014, in Tokyo’s Arakawa Ward.

Six days earlier she had attempted to strangle the boy inside a restroom at a hotel in the ward where the family was staying. For this incident, she was charged with attempted murder but the court ruled that there was doubt as to whether she had intended to kill her son, and instead decided she was guilty of causing bodily injury.

Prosecutors had sought a 15-year prison term for Kato, arguing that she did not love her son and found taking care of him stressful, leading her to repeated shoplifting offenses and leading her husband to threaten divorce if she shoplifted again.